The need to remain competitive in cost and performance in the production of semiconductor devices has caused a continuous increase in device density of integrated circuits. To accomplish higher integration and miniaturization in a semiconductor integrated circuit, miniaturization of a circuit pattern formed on a semiconductor wafer must also be accomplished.
Conventionally, circuit patterns are formed on semiconductor substrates using radiation-sensitive materials, such as photoresists, to fabricate an imaged pattern therein. The process of fabricating an imaged pattern includes forming layer of photoresist material on a semiconductor substrate, possibly followed by heating the layer of photoresist material to, for example, evaporate any solvent. The layer of photoresist is then subjected to a patterned exposure of radiation. After an optional post-exposure bake is performed, the exposed region of the layer of photoresist is developed using a basic developing solution. A deionized (DI) water rinse may wash away any undissolved particles left after the developing solution treatment to provide a patterned layer of photoresist on the substrate. Spin drying may be subsequently employed to remove any remaining droplets of deionized water. However, while this process for fabricating a patterned layer of photoresist is well-known and practiced, it does have its shortcomings as features get smaller and closer together.
For example, one shortcoming is the increased incidence of pattern collapse. Design rules, such as critical dimensions (CD), define the space tolerance between devices or interconnect lines so as to ensure that the devices or lines do not interact with one another in any unwanted manner. But an effect of decreasing critical dimension size is a corresponding increase in the force that causes pattern lines to collapse, as shown in the following relationship:F=6·γ·cos θ·(H/W)2·(1/S)  Equation 1wherein F is the collapse force, is the surface tension of the rinsing liquid; θ is the contact angle of the rinse liquid on the material surface; H is the height of the line; W is the width of the line; and S is the spacing between the lines. As shown in Equation 1, increasing the height (H) of the line, decreasing the width (W) of the line or decreasing the spacing (S) between the photoresist lines produces an increase in the collapse force (F). Similarly, decreasing the contact angle (θ) or increasing the surface tension (γ) of the rinsing liquid produces an increase in F. Herein, collapse force F is expressed in units of force per unit area, i.e. it is the bending stress to which the pattern is exposed during rinse.
Moreover, as a critical dimension gets smaller, the aspect ratio (H/W) of the pattern lines generally increases because the thickness (height) of the radiation-sensitive composition (e.g., photoresist) is generally based on factors such as etch resistance. Thus, it would appear that miniaturization of line patterns inherently increases the collapse force (F).
As such, several approaches toward reducing the collapse force (F) have focused on modifying the surface tension (γ) of the rinsing liquid. Tanaka et al., U.S. Pat. No. 5,374,502 and Reynolds, WO2005/010620 describe methods of using rinse liquids that contain one or more aliphatic alcohols, such as isopropanol, butanol, or pentanol. But these methods can produce over-development of the photo-resist layer or cause the collapse of the photo-resist line by dissolving the layers beneath the photo-resist layer. Lee et al., U.S. Pat. No. 7,238,653 describes using a surfactant, such as a phosphate-alcoholamine salt, to reduce the surface tension of the rinsing solution. But because a phosphate-alcoholamine salt is not volatile, the rinsing solution will leave a residue upon drying. So a cleaning rinse with DI water, which has high surface tension, would be necessary to remove the surfactant residue.
In view of the foregoing, there is a need for new methods of reducing pattern collapse.